Article,
Seismic velocity and attenuation structure of the Geysers geothermal field, California
Geothermics, 23 (2): 111--126 (April 1994)
DOI: 10.1016/0375-6505(94)90033-7
Abstract
The Geysers geothermal field is located in northern California and
is one of the world's largest producers of electricity from geothermal
energy. A key resource management issue at this field is the distribution
of fluid in the matrix of the reservoir rock. In this paper, we interpret
seismic compressional-wave velocity and quality quotient (Q) data
at The Geysers in terms of the geologic structure and fluid saturation
in the reservoir. Our data consist of waveforms from approximately
300 earthquakes. Using compressional-wave arrival times, we invert
for earthquake location, origin time, and velocity within a three-dimensional
grid. Using the pulse width of the compressional wave, we invert
for the pulse width contribution associated with the source and the
one-dimensional Q structure. We find that the velocity structure
correlates with known mapped geologic units. The dry steam reservoir,
which is known from steam well drilling, is mostly correlated with
low velocity. The correlation is best for those areas where the steam
pressure has been reduced by production. The Q increases with depth
to the top of the dry steam reservoir and decreases with depth within
the reservoir. This decrease of Q with depth suggests that the liquid
saturation of the reservoir rock matrix increases with depth.
